1. Field of the Invention
The invention relates to a method for controlling A-shaped segregation by purification of liquid steel.
2. Description of the Related Art
In the process of manufacturing steel ingots, casting defects including macrosegregation, large non-metallic inclusions, and central porosity often exist, thereby seriously affecting the forging quality. The macrosegregation, particularly A-shaped segregation (V-shaped segregation often occurs in continuous casting), is the worst defects that significantly affect the performance of products, and cannot be eliminated. Thus, a simple and practical method for solving the A-shaped segregation is desired. In A-shaped segregation regions, a large amount of inclusions exist, so that it is important to overcome the defects of the inclusions in the steel ingots. For some certain steel, for example, rotor steel, inclusions like Al2O3 and MnS in the A-shaped segregation critically influences the mechanical property of the steel, and becomes a source of fissures, thus, to decrease the A-shaped segregation in the steel ingot is conducive to improving the quality of forged pieces.
The A-shaped segregation region is accumulated with carbon, sulfur, phosphorus, oxides, sulfides, and gas, thereby producing much more abandoned products. A typical method for solving the A-shaped segregation in the steel ingot includes: introducing a foreign cooling matter, or external field treating, or intensifying external cooling of the steel ingot to fast solidify of the steel ingot or the blank, thereby eliminating or decreasing the A-shaped segregation. However, the method is difficult to operate and is inapplicable in the preparation of large steel ingot or blank Furthermore, it is possible to introduce large inclusions, thereby directly resulting in the abandonment of the steel ingot. Thus, it is necessary to develop a new method for tackling the A-shaped segregation problem in preparation of large steel ingot or large cross sectioned continuous casting blank. It has been found based on computer analogy, real time observation by X-ray, and physical anatomy that a main source of the A-shaped segregation is the inclusions, particularly Al2O3 and MnS. Although slowly flowing of interdendritic fluids facilitates the formation of the A-shaped segregation, it is not the origin of the A-shaped segregation.